Negative active material for secondary battery and method of manufacturing the same

Abstract

A negative active material for a secondary battery that provides high capacity, high efficiency charging and discharging characteristics includes: a silicon single phase; and a silicon-metal alloy phase by which the silicon single phase is bounded, wherein the negative active material comprises 5 to 30 wt % of nickel, 5 to 30 wt % of titanium, and 40 to 90 wt % of silicon, the negative active material has a first peak of the silicon-metal alloy phase in an X-ray diffraction analysis spectrum, the silicon single phase is finely distributed in the silicon-metal single phase by mechanical alloying, and the first peak resulting from the (501) surface of the silicon-metal alloy phase has a greater value than the first peak resulting from the (501) surface of the silicon-metal alloy phase that is not subjected to the mechanical alloying, by 0.6° to 0.9°.

What is claimed is: 
     
         1 . A negative active material comprising:
 a silicon single phase; and   a silicon-metal alloy phase by which the silicon single phase is bounded,   wherein the negative active material comprises 5 to 30 wt % of nickel, 5 to 30 wt % of titanium, and 40 to 90 wt % of silicon,   the negative active material has a first peak of the silicon-metal alloy phase in an X-ray diffraction analysis spectrum,   the silicon single phase is finely distributed in the silicon-metal single phase by mechanical alloying, and   the first peak resulting from the (501) surface of the silicon-metal alloy phase has a greater value than the first peak resulting from the (501) surface of the silicon-metal alloy phase that is not subjected to the mechanical alloying, by 0.6° to 0.9°.   
     
     
         2 . The negative active material of  claim 1 , wherein the first peak results from a (501) surface of Ni 4 Si 7 Ti 4  and appears at 40.3±0.15 degrees (°). 
     
     
         3 . The negative active material of  claim 1 , wherein
 the first peak resulting from the (501) surface of the silicon-metal alloy phase has a greater value than the first peak resulting from the (501) surface of the silicon-metal alloy phase that is not subjected to the mechanical alloying, by 0.7° to 0.8°.   
     
     
         4 . The negative active material of  claim 1 , wherein
 the first peak resulting from the (501) surface of the silicon-metal alloy phase shifts more on the right hand side in X-ray diffraction analysis spectrum than the first peak resulting from the (501) surface of the silicon-metal alloy phase that is not subjected to the mechanical alloying by 0.6° to 0.9°, due to shrinking of a lattice in a direction perpendicular to the (501) surface by performing mechanical alloying comprising high energy milling.   
     
     
         5 . The negative active material of  claim 1 , wherein
 the first peak resulting from the (501) surface of the silicon-metal alloy phase shifts more on the right hand side in X-ray diffraction analysis spectrum than the first peak resulting from the (501) surface of the silicon-metal alloy phase that is not subjected to the mechanical alloying by 0.7° to 0.8°, due to shrinking of a lattice in a direction perpendicular to the (501) surface by performing mechanical alloying comprising high energy milling.   
     
     
         6 . The negative active material of  claim 1 , wherein
 the negative active material comprises 10 to 30 wt % of nickel, 10 to 30 wt % of titanium, and 40 to 80 wt % of silicon.   
     
     
         7 . The negative active material of  claim 1 , wherein
 a size of the silicon single phase obtained from the X-ray diffraction analysis spectrum is smaller than 20 nm.   
     
     
         8 . The negative active material of  claim 1 , wherein the negative active material further has a second peak of the silicon-metal alloy phase in an X-ray diffraction analysis spectrum. 
     
     
         9 . The negative active material of  claim 8 , wherein the second peak results from a (501) surface of Ni 4 Si 7 Ti 4  and appears at 40.83±0.1 degrees (°). 
     
     
         10 . A method of preparing a negative active material that is used in a secondary battery and comprises a silicon-metal alloy powder,
 melting silicon and metal to form a molten mixture;   solidifying the molten mixture by rapid cooling to form a ribbon-shape rapid cooling solidification product; and   milling the rapid cooling solidification product by using a high energy milling apparatus so that alloy powder is formed and simultaneously, a silicon single phase is fragmented in the alloy powder,   wherein a size of the silicon single phase in the alloy powder is smaller than 50 nm.   
     
     
         11 . The method of  claim 10 , wherein
 the high energy milling apparatus comprises at least one selected from a high energy ball mill apparatus, an agitating ball mill apparatus, an oil-based ball mill apparatus, and a vibration ball mill apparatus.   
     
     
         12 . The method of  claim 10 , wherein
 the milling the rapid cooling solidification product by using a high energy milling apparatus is performed for 4 to 6 hours.